Nick Clegg, the deputy prime minister, today promised plans that require MPs to deliver a 55% majority to force an early dissolution of parliament will be adjusted to limit the risk of "limbo" in the Commons.

In pursuit of a fixed-term parliament, the coalition has proposed that there would need to be a 55% majority before parliament could be dissolved, but the idea continued to draw protests from Tory backbenchers, including the former shadow justice minister Eleanor Laing.

Clegg insisted yesterday a government would fall if it lost a confidence vote on a simple majority, and it would not continue indefinitely if a new government could not be formed. Officials suggested there would be a time limit put into the legislation, so that if no potential prime minister could gain majority support, and yet there was not 55% support for the dissolution of parliament, the parliament would eventually be dissolved.

He promised: "We will set out how we can avoid a limbo where a government does not enjoy the confidence of this House and yet a vote cannot take place to dissolve parliament."

Other constitutional announcements by Clegg included:

• A three-party, nine-strong committee of MPs and peers will start work next week charged with producing a draft bill on an elected second chamber by the end of the year, ahead of pre-legislative scrutiny by a committee from both houses.

• The insertion of a quasi-judicial figure before MPs on the standards committee declare an MP's misconduct has been so serious that the electorate should have a right to petition for a by-election.

• A commitment that a constituency boundary review designed to reduce the total number of MPs by a modest amount will take into account the geography of a region, and not insist solely on "a rigid arithmetical formula to ensure a number of voters per constituency". He said in the last election one in five English constituencies were more than 10% above or below the target figure of 69,000 electors.

• A promise to speed up Labour plans to move to compulsory individual registration of voters before 2015, which will be backed by extra resources. At present as many as 3.5m voters in Britain regarded as eligible to vote are not registered.

•A commitment that a referendum on extra powers for the Welsh assembly will be held early next year. Clegg's office later accepted that he had inadvertently misled parliament by saying the coalition as a whole would support the assembly having extra powers.

• Abandonment of David Cameron's plans announced in the election campaign that a general election will be held within six months of a party changing the prime minister.

But in a sign of debates inside the coalition, Clegg was unable to give a date for the promised referendum on the Alternative Vote for electing MPs, or whether the legislation required for the referendum will be included in a wider political reform bill, or instead rushed through in a separate bill .

Senior Liberal Democrats favour a referendum next May, the same date as the local elections, but there are fears that if the referendum is lost the glue holding the coalition together would weaken.

Cameron said at the weekend he will simply state his personal belief in first past the post, but other Tory cabinet members are said to be warming towards AV, admitting they have been intellectually lazy in looking at the virtues of other electoral systems.

Clegg's advisers said the Liberal Democrat leader, in contrast to Cameron, will campaign actively in favour of the change. He said the coalition was determined to produce reforms to the Lords that are more than 100 years overdue. "People have been talking about Lords reform for over a century. The time for talk is over. People should be allowed to elect those who make the laws of the land. Change must begin now."